linux-kernel - Re: [RFC PATCH 2/5] clk: Introduce 'clk_round_rate

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Date:	Tue, 20 May 2014 10:48:43 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Mike Turquette <mturquette@...aro.org>,
	linux-pm@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Michal Simek <michal.simek@...inx.com>,
	cpufreq@...r.kernel.org, linux-kernel@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 2/5] clk: Introduce 'clk_round_rate_nearest()'

On 05/20/14 09:01, Sören Brinkmann wrote:
>
>>>>> +{
>>>>> +	unsigned long lower, upper, cur, lower_last, upper_last;
>>>>> +
>>>>> +	lower = clk_round_rate(clk, rate);
>>>>> +	if (lower >= rate)
>>>>> +		return lower;
>>>> Is the >-case worth a warning?
>>> No, it's correct behavior. If you request a rate that is way lower than what the
>>> clock can generate, returning something larger is perfectly valid, IMHO.
>>> Which reveals one problem in this whole discussion. The API does not
>>> require clk_round_rate() to round down. It is actually an implementation
>>> choice that had been made for clk-divider.
>> I'm sure it's more than an implementation choice for clk-divider. But I
>> don't find any respective documentation (but I didn't try hard).
> A similar discussion - without final conclusion:
> https://lkml.org/lkml/2010/7/14/260
>
>

Please call this new API something like clk_find_nearest_rate() or
something. clk_round_rate() is supposed to return the rate that will be
set if you call clk_set_rate() with the same arguments. It's up to the
implementation to decide if that means rounding the rate up or down or
to the nearest value.

-- 
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